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Plant Structure
Chapter 18

I. Tissues

A. Meristematic- regions of cell division (Mitosis)

1. thin walled cells
2. no vacuoles
3. grow tips of stems and roots (apical meristems)
4. vascular cambium- plants that grow in width (woody plants)

B. Protective

1. epidermis- outer layer on leaves, green stems, roots
2. cuticle (cutin)- waxy layer on epidermis to prevent water loss
3. cork- covers woody stems and roots

a. formed from meristematic cells- cork cambium
b. at maturity, cork cells are dead

C. Vascular- conducting tissue

1. xylem- conducts water and minerals up from the roots to the leaves

a. mature cells are dead, contain no cytoplasm
b. form continuous tubes from the roots up
c. composed of two types of cells

i. tracheids- contain pits in the cell wall
ii. vessel elements- conducting tubes

d. wood

2. phloem- conduct organic materials dissolved in water in water up and down the plant

a. alive
b. composed of two types of cells

i. sieve cells- form sieve tubes for conduction
ii. contain cytoplasm but no nucleus at maturity

c. companion cells- control the passage of materials in the sieve tubes

D. Fundamental- involved in the production and storage of food

1. parenchyma- unspecialized cells, thin cell walls, photosynthesis, food storage
2. collenchyma- strengthen support stems, leaves
3. sclerenchyma- strengthen, support, fibers, xylem, phloem

II. Roots- anchors the plant, absorbs water minerals, stores food, excretes wastes

A. Types

1.primary root- first structure to emerge from a sprouting seed
2. secondary root- branches from the primary root

B.Root systems

1. taproot- a system that grows from the primary root
2. fibrous- made up of numerous roots, all are the same size
3. adventitious- do not originate from the primary root

a. climbing roots
b. air roots

C. Root tip zone

1. root cap- protective covering of the meristematic tissues
2. meristematic zone- region of actively dividing cells behind the root cap
3. elongation zone- behind the meristematic zone, enlarge & push the root tip forward
4. maturation zone- behind the elongation zone, cells differentiate (become specialized)

D. Structure and function

1. root hairs- epidermal cells, increase surface area for absorption
2. cortex- parenchyma, store food, transport water
3. endodermis- control the movement of water into the central cylinder
4. central (vascular) cylinder- surrounded by ring of parenchyma cells called pericycle (where all secondary roots originate)
5. at the center of the vascular cylinder is the xylem and phloem

III. Stem

A. Woody stems- thick, wood
B. Herbaceous stems- soft, green, juicy
C. Monocot stem- have one cotyledon (seed leaves)

1. herbaceous monocots- corn

a. vascular bundles are scattered throughout the tissue of the stem
b. no cambium present, little stem diameter growth

2. woody monocot stems- similar to herbaceous monocot stems except the stems become woody by the thickening of the walls of the parenchyma cells

D. Dicot stems- contain two cotyledons

1. herbaceous stems

a. vascular bundles are arranged in a ring inside the cortex (made of xylem & phloem)
b. pith- central region of stem, parenchyma cells that store food

2. woody dicot stems

a. external structure:

i. terminal bud- tip, contain meristem (contains auxins)
ii. leaf scars- points of attachment of leaves from previous season
iii. lateral bud- can form new branch
iv. nodes- point along the stem where leaves & lateral buds form
v. internodes- space between lateral buds
vi. lenticels- holes in stems for gas exchange

b. internal structure- annual rings (growth of new xylem during the growing season)

i. spring wood, summer wood (differences in color)
ii. heartwood- older, inner, dark colored region of xylem does not conduct water
iii. sapwood- light colored xylem
iv. bark- protective tissue

E. Differing Characteristics between Monocots & Dicots

Monocots

Dicots

seed leaves

one cotyledon

two cotyledon

leaf venation

parallel veins

net like veins

stems

bundles scattered

bundles in rings

flowers

flower parts usually in three

flower parts usually in fours & fives

IV. Leaf- site of photosynthesis

A. External Structure

1. blade- leaf
2. petiole (stalk)- attaches leaf to stem
3. veins- vascular tissue [located in the mesophyll layer]

B. Internal Structure

1. epidermis- protection (one cell thick)

a. cuticle- waxy layer, prevents excess water loss
b. stomates- opening in the epidermis for gas exchange
c. guard cells- regulate the opening & closing of the stomates

2. mesophyll- middle layer, photosynthetic layer

a. palisade layer- upper layer of the mesophyll, contains chloroplasts
b. spongy layer- consists of irregularly shaped cells separated by large air spaces, contain less chlorophyll

Biology Trivia

1. What is the most widely eaten tuberous root? answer

2. What is the world's largest flower? answer

3. What is the tallest tree? answer